In a known valve apparatus, a valve member includes a head engagable with a seat in a valve body to shut off flow through the flow passage in the valve body. The valve member includes a stem which carries the head and is reciprocable with respect to the valve body. To prevent fluid in the passage from escaping along the valve stem, it is conventional to provide an annular seal, e.g. a conventional packing, fixed with respect to the valve body and through which the valve stem is snugly reciprocable.
It is known to provide a bellows surrounding the valve stem and extending axially from the valve head to a portion of the valve body adjacent the packing. In this way, even with the valve open, particles or other harmful materials in the fluid passing through the valve body are prevented by the bellows from contacting the valve stem and the packing.
Applicant has found that a metal bellows may be more durable in such service than bellows of rubber or similar materials. Whereas formed metal bellows are known, Applicant has found that a welded metal bellows, for example of the type disclosed in U.S. Pat. No. 3,090,403 to Kroekel, has greater expandability than a formed bellows and tends to have less stress built into it. However, Applicant has also recognized that the relatively thin leaves of such a welded bellows could be damaged, even holed, during compression of such a bellows with a hard particle interposed between adjacent leaves of the bellows.
To avoid the latter problem, Applicant's invention provides additional sealing means between the reciprocable valve head and fixed valve body to substantially prevent fluid, from the main passage in the valve body, from reaching the bellows even with the valve member in its open condition. Moreover, Applicant's same inventive sealing means protects the bellows from water hammer or other shocks caused by implosion, explosion or shocks within the fluid passing through the valve, which shocks may, for example, be due to slamming check valves, etc. nearby in a fluid circuit containing the inventive valve apparatus. In addition, Applicant's inventive sealing means acts as a further backup seal to prevent fluid in the valve passage from contacting, and leaking outward past, the valve stem.